Among the known elementary particles only neutrinos undergo the phenomenon of flavor oscillations [1]}, [2]}. The quantum field theory (QFT) of fermion mixing, which is adequate to the description of mixed neutrinos, shows a very rich structure both in flat [3]}, [4]}, [5]}, [6]} and in curved spacetime [7]}. In virtue of the peculiar condensate structure of the flavor vacuum, this theory may have interesting cosmological consequences [8]}, [9]}, [10]}, [11]}, [12]}. Simulations of the QFT of flavor mixing, in the context of atomic physics, have also been proposed [13]}. The mixing of bosons is, in some respects, more exotic. The bosons which are known to mix are indeed composite particles subject to decay, i. e. the mesons \(K, B, D\)  [14]}, [15]}, [16]}, [17]}, [18]}, [19]}, [20]}, [21]}, [22]}, [23]}, [24]}, [25]}, [26]}, [27]}, [28]}. Other schemes of boson mixing may arise under specific conditions for hypothetical particles, as it is the case of the mixing of photons with axionlike particles in presence of an external magnetic field [29]}, [30]}. One can additionally speculate that the supersymmetryc bosonic partners of neutrinos [31]}, [32]} would mix in analogy with their fermionic counterparts. The QFT of boson mixing, developed in flat space in ([33]}, [34]} and references therein) is then interesting in order to provide a solid field theoretical foundation to the phenomena mentioned above. Just like the QFT of fermion mixing, the QFT of boson mixing presents a rich mathematical structure and a nontrivial vacuum state. Previous analyses have shown that the latter may contribute to the dark components of the universe, in a clear analogy with the fermion flavor vacuum [9]}, [10]}.
